This invention relates to a method of providing elastomer compositions including a peroxide curable elastomer gum, notably a fluoroelastomer gum, a solid particulate filler, and a coupling agent for strengthening the bond between the polymer and the filler upon curing.
Fillers for elastomers are of two general types, reinforcing and non-reinforcing. A non-reinforcing filler increases the bulk of an elastomer and may cause a decrease in properties such as modulus and tear strength. Reinforcing fillers such as carbon black, silicas, metal oxides, and the like improve properties of elastomers in which they are incorporated, thus providing elastomers having more desirable characteristics than corresponding unfilled elastomers. The use of a suitable coupling agent can improve the efficacy of such reinforcing fillers, providing elastomers with improved mechanical strength at elevated temperatures, better resistance to solvent swelling, and greater resistance to failure at the filler/polymer interfaces.
The concept of employing a coupling agent to improve bonding between a solid, particulate filler and the cured matrix of an elastomer has been described. An example of the use of coupling agents is the treatment of finely divided silica with a difunctional silane having at least one functional group reactive with silanol groups on the silica and at least one functional group such as a mercapto group, reactive with the elastomer matrix in which the filler is incorporated. Many sizes and coatings have been developed to improve bonding between rubber and plastic, steel, or fiber-glass filaments, strands, cloth, and the like.
Fluorinated elastomers are becoming increasingly important in applications requiring resistance to fuel, oil, and hydraulic fluids, low compression set, and retention of flexibility upon exposure to higher temperatures. They were first used in aircraft seals and have come into use in the chemical, petrochemical, and automotive industries. Fluoroelastomers have excellent resistance to hot oils, synthetic lubricants, gasoline, jet fuels, dry cleaning solvents and other organic solvents. Certain formulations are resistant to hot mineral acids, steam, hot water, certain alkalis, and a number of organic acids. They burn in a direct flame but otherwise have low flammability.
Fluoroelastomers can be injection molded, transfer molded, compression molded, or extruded to form such articles as O-rings, molded packings, oil seals, tubing, hose gaskets, mechanical goods, and rubber rolls.
It has been known to employ a variety of carbonaceous and inorganic reinforcing fillers in fluoroelastomers, including carbon black, finely ground coal, silica, iron oxide, zinc sulfide, calcium carbonate, and barium sulfate. Such fillers provide cured fluoroelastomers having improved mechanical properties such as tensile strength, tear strength, compression set, and the like. Further improvement through the use of a coupling agent has not thus far been described.